Telephone system.



I No.- 719,998.

EAT NTED EEE. 10,1903.

E. E. CLEMENT. TELEPHONE SYSTEM.

APPLICATION FILED JUNE 4, 1901.

no MoD Ll UNITED STATES PATENT OFFICE.

EDWARD E. CLEMENT, OF PHILADELPHIA, PENNSYLVANIA.

TELEPHQNE SYSTEM.'

SPECIFICATION forming part of Letters Patent No. 9,998, dated February10, 1903.

Application filed June 4, 1901. Serial No- 63,052. (No model.)

To all whom it may concern:

Be it known that I, EDWARD E. CLEMENT, a citizen of the United States,residing in the city and county of Philadelphia, State of Pennsylvania,have invented a new and useful Improvement in Telephone Systems, ofwhich the following is a specification.

' My invention relates to telephone systems in general and to exchangesystems employing a common battery at the central office in particular.In such systems it has heretofore been necessary to provide means at thesubscribers stations to satisfy the following conditions: line not inuse and not being ca1ledcircuit open at subscribers station anddirect-current generator on the line at central; line beingcalled--alternating-current generator connected at central, and a pathclosed for same at subscribers station, but open to direct current; linein use-circuit closed at subscribers station for direct current andmaintained so until completion of the conversation; line disconnected atcentral from main-battery busses and connected through cord conductorsto battery. In considering these conditions it is seen at once that theprincipal problem is that of differentiating between the direct andalternating currents that are applied to the line for calling in andcalling out, respectively. To do this it has heretofore been the customto use condensers in series with the ringers, and when the subscriberremoves his receiver from its hook for a call or to answer a call tocause the ringer and condenser to be cut out or to be brought into suchrelation with the transmitting and receiving mechanism as not tointerfere with the transmission of speech. According to one plan, theringer and condenser are normally bridged across the line- Wires, andthe transmitter, receiver, and induction-coil are cut out. In using thetelephone the hook rises and brings the ringer into parallel with theprimary and secondary windings of the induction-coil in series and thecondenser into a shunt of the transmitter and in series with one windingof the coil and the receiver. The condenser in that case acts to sharpenthe variations in current sent to line during conversation as well as tohold the line open at other times. Such a condenser should have acapacity of approximagnets.

mately two microfarads and should stand a potential of one hundred voltsor more without breakdown. Even a hundred-volt condenser will not alwaysstand the strain put upon it by a large ringing generator, however, andin order to secure freedom from troubles it is necessary to exertconsiderable care in the manufacture, with the result that the averagecondenser in place represents considerable money.

It is the object of my invention to do away with condensers entirely atsubscribers stations, bringing the apparatus down to thesimplestelements. Theswitch-hook becomes one with a single contact or atmost two contacts. scheme, I have devised the circuits and apparatus atcentral or simplified to do away with the necessity for the lastcondition named above, leaving the lines permanently connected to themain busses.

In attaining my object I employ in place of the condensers what havebecome well known under the name of coherers in other connections-thatis, instead of maintaining a path open to direct current, but closed bystatic induction for the passage of alternating or changing currents, Iemploy a device in series with my ringer that is normally open for allpractical purposes to any currents and unaffected by a considerableelectromotive force if the same is steadily applied. When electromotiveforces are impressedon the line,however, which are sharply varied oralternated, or when discharges are induced in the line that are more orless disruptive in their nature, the device will suddenly becomepassable to current of any kind and furnish a conductively continuouspath for the ringing-current through the ringer- I believeI am the firstto discover that alternatingcurrents having certain wave forms have theproperty of acting through poor contacts or coherers, so called,lowering their resistance during their passage and, according to thecharacter of the coherers, leaving them at normal high resistance, ifself-decohering, or low resistance, as the case may be; that I am thefirstto use the same current both for cohering and for signaling throughthe coheror and the first to produce Moreover, as apart of the general adevice of any form which will offer great resistance to the passage ofone kind of current, will respond to other forms of current or impressedelectromotive forces resulting in currents by an internal actionlowering or altering the said resistance, and thereby pass the currentproducing the change to affect ordinary translating devices, such assignals and the like. It has heretofore been supposed, before mydiscoveryand invention, that it was impossible to construct a cohererthat would have any substantial currentcarrying capacity, and the use ofa coherer in the same way as a relay of the ordinary type has beenconfined to very high potential primary transmitting-circuits, usuallyconveying electrical jerks of a highly discontinuous nature, while theuse as a substitute for a condenser has not only been undiscovered, but,if thought of, would have been considered far from feasible. I claimthat I have made another agency available which will be of greatpractical service in the electrical art, and I wish it to be understood,therefore, thatIseek to cover, broadly, all forms of apparatus andsystems in which my discovery may be employed, Whether so contemplatedspecifically by me at the present time or not.

My invention is illustrated in the accompanying drawings, wherein thesame characters of reference represent the same parts throughout.

Referring to the drawings, Figure 1 is a diagram of a complete system ofconnected circuits employing my invention. Fig. 2 is a side view of oneform of switch-hook. Fig.

- 3 is a similar view of a ringer with the coherer mounted upon it. Fig.4 is a modification, to be described.

Referring to Fig. l, X and Y are two subscribers stations, and W is acentral office. The subscribers lines 1 2 3 4 are permanently connectedto the main-battery busbars 15 16, the battery being lettered B. Atstation X, T is the transmitter, R is the receiver, S is theswitch-hook, Q is the ringer, and C is the coherer. Instead of includingthe receiver R directly in the line I avoid the pull on the diaphragmwhich the line-current causes by placing the receiver in the localcircuit of a coil 1, having its primary t" in the line and its secondaryt' in the local.

On the switch-hook S, I mount. the coherer, so that the movement of thehook when the receiver is removed or replaced will jar thecohereranddecoherer. Thedetailsofthemounting are shown in Fig. 2. Thehook proper, S, is pivoted by means of a shoulder-screw s on a plate 5having perforations s for attachment tothe casing of the telephone andan upturned lip 3 upon which a set of springs s S s are mounted. A'larger spring 3 is mounted beneath the others, having. the purelymechanical function of keeping the hook S elevated.

s is a slotted escutcheon'plate in which the mates hook oscillates.Mounted onthe side of the hook are two blocks of hard rubber 0 0 betweenwhich is supported, preferably by having its ends set in the blocks, atube C, of glass or other suitable insulating material, with terminals 0o sealed into it and spaced far enough apart to receive asmall quantityof metallic filings, preferably ironand nickel mixed and rather coarseof grain. Terminals for wires are led out from the tube through therubber blocks at c c, the connectingwires not being shown in the figure.By this construction it will be understood that every time the hookrises sharply against the upper end of the slot in the escutcheon andevery time it is depressed in a similar manner by the receiver thecoherer is shaken up and the filings are restored to their condition ofhigh resistance.

Returning now to Fig. 1, the hook at station X is shown down and theringer Q and coherer in circuit. The talking-set is out out. The normalresistance of coherers for this purpose, asI have determined to usethem, is one hundred thousand ohms, approximately. This is a purelyarbitrary figure, as it may be more or less Without prejudice. With sucha resistance, however, and the usual voltage at central in themain-battery circuit the leakage atany station is about .024.milliamperes, a little over one-fiftieth of a milliampere, which is anegligible quantity, even when multiplied by the largest number of linesnot calling and idle in alarge exchange. In other words, the circuitsare normally open for all practical purposes. The conditions aretherefore substantially the same as where a condenser is used for theringer-circuit.

At the central office, B is the main battery, connected across bus-wires15 16, to which all the line-wires are permanently connected.

L is the line-signal of the station X, and L a balancing-coil.Similarly,L is the line-signal of the station Y, and L is itsbalancingcoil. It is desirable to maintain the lines perfectlybalanced,especially in a multiple-board system, toprevent cross-talk andother disturbances.

J is the line-jack of line 1 2, having a pair of contactsj 7", and,similarly, J is the jack of line 3 4;. Multiple jacks are also shown;but as they are not necessary to the consideration of the presentinvention they are not lettered. In the other applications to which Ihave made reference, however, the details of the present system aregiven in full.

P P are a pair of plugs connected by the cord conductors 17 18 19 20.

The operation ofthe system shown in Fig. 1 may now be understood.Suppose the subscriber at X is desirous of calling Y. He removes hisreceiver from the hook and the circuitB 15L2 9 T 7; 8 s S l L 16 isclosed. Line-signal L is therefore displayed. The operator inserts plugP in jack J, and line-signal L immediately is retired. The operator nowcuts herself in by the key K and, ascertaining the number wanted,insertsplug l? in jack J. Then by depressing key K she putscalling-generator G on the plug P and so to line 3 4:. The efiect of thealternating current on the coherer O is greatly enhanced by having thecoils L L in parallel and the condenser Z in circuit. Such a conditionis not absolutely essential, however. The coherer responds to the firstalternations by breaking down in resistance, so that the ringing-currentpasses to the ringer Q in the branch 12 13 through a low resistancewhich is non-inductive. The resistance of the average coherer whencohered can be brought as low as forty ohms.

lever h is raised and allowed to fall so that its tip strikes a tap onthe coherer-tube, causing the filings to fall apart and decohere. At theconclusion of the conversation, when the subscribers have hung up, bothcoherers are again shaken up, that at X by the jar of the hook directand that at Y by the lever it. During conversation the current fromgener ator B passes to both lines in parallel, and K is a listening-keyto connect the operators set 0 across the cord, and K is a ringing-keyto connect the ringing-generator G through its circuit 23 24 to theconductors 19 20, at the same time disconnecting the latter from theanswering-plug P.

In order to enhance the efiect of the ring ing-generator G on thecoherers, it is sometimes desirable to include a condenser Z in thegenerator-circuit, as shown. This is not an indispensable adjunct,however. I

At station X in Fig. 1 I have shown the coherer carried on theswitch-hook and jarred by the latters movements to decohere. At stationY, 1 show a different arrangement. Here the coherer is supportedindependently, the hook having up and down contacts 8 and s, so thatwhen it rises the coherer and ringer are disconnected at the latterpoint, and a tapper h is shown worked by the hook to strike the cohererwhen the hook moves. I do not limit myself to any particular form oftapper, as many forms will suggest-themselves toany one familiar withthe various forms of coherers in use; but the tappermust be workable inboth movements of the hooki. 6., when it goes down as well as when itgoes up-for the reason that when the ringer and coherer are thrownacross the line after completion of a conversation the coherer must havebeen restored to its normal high resistance or there will be falsesignals given at central, or, at least, serious leakage from the mainbattery. I have therefore indicated a bell-crank lever having one armprovided with a projection adapted to be raised by a similar projectionon the switch-hook when it moves in either direction. The variations dueto changes in the transmitters are conveyed through the cord conductorspast the generator, being prevented from passing the bridge by thechoke-coils g g. i 1

tion reliable under all conditions.

When the subscriber answers, he takes the receiver from the hook, andthe In some cases the arrangement shown in Figs. 2 and 3 Ihave shownmodifications intended to make the coherer action and inac- Thusatmospheric discharges or induced charges on the lines from other lines,as well as disturbances due to crosses, might cause the coherers to act,and in such cases the resistances being brought low enough to becomparable to that of the transmitter and receiver circuit thebattery-current would flow, giving false signals at L MD, as well aswasting the current. The latter would be the most undesirable condition,as in theformer case, if not too frequent of occurrence, the operatorcould call up and getthe hook moved to decohere. In the case ofcontinuous leakage, however, if the resistance of the ringer and cohererdid not permit sufficient flow to energize the line-signal there wouldbe no means of determiningthe trouble, or, at least, of loeating it,without testing every line. There is a possibility also that theapparatus in Fig. 1 might fail to decohere, and this would leave theline closed after every conversation.

The general idea which I adopt to prevent the conditions named is thatof making the decoherer self-acting in its decoherence.

telegraphy a tapper is automatically actuated after every operation; butin the present case I wish to avoid expense, and intermediate relays areto be dispensed with. The preferable arrangement for economy is shown inFig. 3. Here I show the coherer C mounted directly on the frame of theringer Q and subject to all the vibrations caused by the oscillationsofthe armature and hammer. Moreover, the magnet of the ringer has atendency to keep the filings in suspension and there- Of course in itsusual application to wireless fore decohered. The alternations inpolarity of the cores also increase the eifect, as all the filingsemployed are preferably (though not necessarily) magnetic.

By this arrangement every impulse that moves the ringer-armature has tocohere and decohere, so that the statement may be literally taken thatthe ringing is done through the coherer.-

In Fig. 4 I show a method of producing the same elfects as above by aseparate mechanism. Here I provide a magnet M, having an armaturem,carrying a hammer t, adapted to come into sharp collision with a stem0, forming one terminal of a coherer G. This coherer is diiferent inform from those in the other figures. It consists, essentially, of anebonite cup with metal sides or bottom 0 and an insulated central pin 0,the filings being disposed in the cup to bridge the pin and sides.Shaking the cup or striking the pin decoheres. circuit of the cohererand ringer and is made rather sluggish, so that its armature will notrespond to the alternations of ringing-current. When the latter hascaused coherence, the bell Q rings,and, whatever the process The magnetM is included in the may be in the coherer, it continues to ring as longas the generator G is to line. When the key K is released and thegenerator G consequently disconnected, direct current from generator Gis again sent to line. Now, suppose that the coherer is still lowered inresistance. Battery-current will flow through the ringer branch andenergize the magnet M, which will attract its armature, the latterclosing a short circuit around the magnet, as shown, when itis fullyattracted and. at the same time striking a blow on the coherer todecohere it. If the decoherence takes place, current is cut off and thearmature 1% falls back. If not, it again pulls up, and the cohererreceives another blow, and so on until decoherence follows.

I wish it to be distinctly understood that I do not limit myself in anyway in my selection of a coherer, as I may use any of the forms now wellknown or variations thereof. One point only is essentialthat the coherershall not break down under a steady differtage. It should also whencohered have a sufficient safe carrying capacity to take the amperagepermitted by the ringer-coils. This I secure by using terminals 0 c ofconsiderable size and coarse filings in somewhat greater quantity thanin the Wireless art. The original Lodge and Branly coherers give veryfair results.

Many modifications of the invention herein described will suggestthemselves to those skilled in the art. I wish it distinctly understoodthat I consider my invention generic in that I believe myself to be thefirst to find a method of keeping line-circuits open tosignaling-currents without a condenser and yet leave them in conditionto be closed for signals when required. This applies to groundedcircuits as well as metallic. In toll-lines where grounded circuits areemployed magneto-signaling systems are usually employed; but even insuch systems this invention may find a place if it is desired to keepdirect current ofi the line except under stated conditions. Inconnection with metallic circuits from modern exchanges the inventionsolves a serious problem.

It is to be noted that while I have described alternating current asoperating the ringer at the subscribers station and also as breakingdown the coherer resistance, yet that is not by any means essential. Adischarge of any kind can be used to break down the resistance, and whenthat is accomplished direct current may be employed to ring, suppliedeither from central or at the subscribers station from a local source. Imay use several forms of coherer that have not been referred to, such asthe oxidized copper balls or the suspended oxidized sphere described inthe application before referred to.

In the claimsI shall refer to the cohering device as a disabling device,because it prevents the line or signal from responding tosignaling-currents, resisting the steady electromotive force. I shallrefer to the ringer as a responsive device or a magnetic responsivedevice. Any substituted piece of apparatus that would be-included inthese terms I consider to be included in the scope of my invention; butthis is not to be taken as meaning that I limit myself by the terms.They are used for convenience.

I shall use the words opaque and transparent in the claims in the senseof non-conducting or conducting, respectivelythat is to say, the cohereror equivalent device is opaque to currents when it either completely orsubstantially opposes their passage.

It is transparent when it lowers or removes its opposition.

The expression sensitive resistance device is employed to distinguishfrom the im- Tpedance-coils and condensers that are sometimes used fordisabling devices to pass alternating but not direct currents.

ence of potential up to a considerable vol- What I claim, and desire tosecure by Let- 'ters Patent of the United States, is

1. In a signaling system, two stations and a con nectin gcircuit betweenthem; a responsive device at one station and a source of current at theother, a sensitive resistance device at the first station normallyholding the responsive device out of operative connection with thecircuit, and a source of energy at thesecond station to alter thecondition of the resistance device to bring the magnetic device intooperative connection with the circuit, and to operate the same.

2. In a signaling system, two stations and an intermediateconnecting-circuit, a signalreceiving device at one station and adisabling device normally rendering the same inoperative and the linesubstantially impassable for currents, together with a source of energyat the second station for affecting the disablingv device to render thesignal device operative,

and to operate the same.

3. In a signaling system, two stations and a connecting-circuittherebetween, a signalreceiving device at one station and asignalsending device at the other station, means at the first station torender the signal-receivin g device normally irresponsive and thecircuit substantially impassable for currents; and a source of energy atthe second station to first render the circuit and signal deviceoperative and then to operate the signal.

4. In an electric signaling system two stations, a connecting-circuittherebetween, a signal-receiving device at the first station and adisabling device of relatively high resistance included in its circuit,a source of current at the second station, together with means to affectthe disabling device to break down and reduce its resistance and tocause the actuation of the signal.

5. In a telephone signaling system, two stations and a circuitconnecting them, a magnetic signal device at one station, and a ootwobridges of the line at the subscribers sta-' hering device havingnormally a very high resistance in circuit with said magnetic device, asource of current at the other station to affect the cohering deviceandbreak down its resistance, whereby the current may reach the magneticsignal device and operatively affect the same.

6. In a telephone-exchange system, a subscribers station, a centralstation, and a linecircuit connecting them; a source of current and asignal at the central station; switching means at the subscribersstation for determining a flow of current in the line; a signal and ahigh-resistance cohering device also at the subscribers stationconnected in circuit but normally impassable for current; and means atthe central station to break down the resistance of said coheringdevice, whereby the signal may be actuated.

7. In a telephone-exchange system, a subscribers station, a centralstation, and a line circuit connecting them; a source of current and asignal connected to the line at central, two bridges of the circuit atthe subscribers station, one normally open and including the telephone,the other normally closed and containing a signal device and a coheringdevice whose resistance renders the bridge impassable forsignaling-currents; together with means at the central station to breakdown said cohering resistance when calling.

8. In a telephone-exchange system a subseribers station and a centralstation and a line interconnecting them; a source of current and asignal connected to the line at central;

tion, one normally open and under the control of the subscriber todetermine a flow of current through the line-signal at central, theother normally closed; a signal-receiving device and a coherer in thenormally closed bridge, the resistance of the coherer rendering saidbridge normally impassable for signal-current; and means at central tothrow sharplyvarying electromotive forces on the line to break down thecoherer resistance, whereby current may pass and the signal may beoperated.

9. In a telephone system, two stations and a connecting-circuittherefor, a signal device at one station and a cohering device of nor-'mally very high resistance in circuit with said signal device, and meansat the other station operating through the connecting-circuit to breakdown the resistance of the coherin g device and to actuate the signaldevice.

10. In a telephone system, two stations and a connecting-circuittherefor, two bridges at one station, speech transmitting and receivingmechanism in one bridge, a signal device in the other bridge togetherwith a cohering device of normally very high resistance, and means atthe other station connected to the circuit to reduce the resistance ofthe coherin g device and operate the signal device.

11. In a telephone system, two stations and a connecting-circuittherefor, a signal device at one station and a cohering device ofnormally very high resistance in circuit with said signal device, meansoperable at the other station to reduce the resistance of the coheringdevice and to operate the signal device, and means at the first stationoperated by the normal operation of the station apparatus to restore thecoherin g device to its state of high resistance.

' 12. In a telephone system, two stations and a connecting-circuittherefor, a signal device and a hook-lever at one station and a coheringdevice of normally very high resistance in circuit with said signaldevice, means oper able at the other station to reduce the resistance ofthe cohering device and operate the signal device, and means at thefirst station operated by the movement of the hook-lever to restore thecohering device to its state of high resistance.

13. In a telephone system, the combination with line-terminals, of twobridges across said terminals, a signal device in one bridge togetherwith a coherin g device of normally very high resistance, and speechtransmitting and receiving mechanism in the other bridge.

14. In a telephone system, the combination with line-te1-minals,ofasignal device together with a cohering device of normally very highresistance in one bridge across said terminals,

speech transmitting and receiving mechanism in a normally open secondbridge across said terminals, and a switch to close said open bridge.

15; In a telephone system, the combination with line-terminals, of twobridges across said terminals, a signal device in one bridge togetherwith a cohering device of normally very highresistance, speechtransmitting and receiving mechanism in the other bridge, and means toopen and close the electrical connection from said terminals throughsaid bridges.

16. In a telephone system, the combination with line-terminals,of asignal device together with a cohering device of normally very highresistance in. a normally closed bridge across said terminals, speechtransmitting and receiving mechanism in a normally open bridge acrosssaid terminals, and switching mechanism to open and close said bridges.

17. In a telephone system, the combination with circuitconductors, ofstation apparatus connected to said conductors, a signal device togetherwith a cohering device of normally very high resistance bridged acrosssaid conductors, and means operated by the normal operation of thestation apparatus to decohere said cohering device. 1

18. In a telephone system, the combination with circuit-conductors, ofstation apparatus connected with said conductors, a signaldevicetogether with a cohering device of normally very high resistancebridged across said conductors,and connectionbetween the hookleverof thestation apparatus and said cohering device whereby the movement of saidhook-lever operates to decohere said cohering device. 7

19. In a telephone system two stations and a connecting-circuittherefor, two branch connections of the circuit at one station, a signaldevice and a cohering device in one branch, speech transmitting andreceiving apparatus in the other branch, and means at the other stationto reduce the resistance of the cohering device and operate the signaldevice.

20. In a telephone system, two stations andaconnecting-circuittherefor,aground branch, with a signal device andcohering device of normally high resistance, therein, and speechtransmitting and receiving apparatus for use in connection with thecircuit, at one station, together with means at the other station foroperating the signal device through the cohering device.

21. In a telephone system, two stations and a connecting-circuittherefor, said circuit composed of two conductors, a ground connectioncontaining a signal device and a coheringdevice, and a metallic circuitconnection with speech transmitting and receiving apparatus, at onestation, together with means at the other station to operate the signaldevice through the cohering device.

22. In a telephone system, a metallic circuit having one or moreground-taps connected thereto and containing cohering devices andsignals, speech transmitting and receiving apparatus adapted to beoperated in connection with the metallic circuit, and means to operatesaid signal devices through the coherer or coherers and a ground-return.

23. In a telephone system, a metallic circuit, a central station andsubstations connected to said circuit, signaling devices and. coheringdevices in ground-taps from the metallic circuit, at the substations,and means at the central station to operate said signal devices throughthe cohering devices.

24. In a signaling system, two stations and a connecting-circuittherefor, a signal device at one station and a coh ering device normallyinterrupting the circuit to the signal, and a source of varying currentat the other station adapted .to operate through the connectingcircuitand through the coherer device to actuate the signal device.

25. In a signaling system, two stations and a connecting-circuittherefor, a signal device at one station and a cohering device normallyinterrupting the circuit to the signaling device, and a source ofalternating current at the other station adapted to operate through theconnecting-circuit to break down the re sistance of the cohering deviceand actuate the signal device.

. 26. In a telephone system, the combination with a line-circuit, of twobranches, a signal device in one branch together with a cohering deviceof normally high resistance, and speech transmitting and receivingmechanism in the other branch.

. 27. In a telephone system, the combination with a metallic circuit ofa branchfrom said circuit containing a signal device and a coheringdevice of normally high resistance, and a normally open bridge of said.circuit containing speech transmitting and receiving mechanism, togetherwith a switch to close said bridge for conversation or signalin 28. In atelephone system, a metallic circuit, a normally connected branchcircuit containing a signal device and a cohering device, a normallydisconnected branch containing speech transmitting and receivingmechanism, and switching mechanism to open the normally connected branchand close the normally disconnected branch to line and vice versa, asrequired.

29. An electric transmission system comprising a circuit, means forsupplying to said circuit currents of different characteristics, atranslating device, and a disabling device connected to the circuit,such disabling device being normally opaque to all currents andpreventing the operation of the translating device, but adapted toautomatically change its condition under the influence of some currentsand not others, to become transparent to such currents, whereby suchselected currents may be caused to actuate the translating device.

30. In an electric transmission system, acircuit, means for supplying tosaid circuit currents having different characteristics, a translatingdevice, and a sensitive resistance device connected to the circuit, saidresistance device being normally opaque to all currents, but adapted toautomatically change its condition under the influence of some of thecurrents, though not of others, to become transparent to such selectedcurrents, whereby they may pass and be caused to actuate the translatingdevice.

31. In an electric transmission system, a circuit, means for supplyingto said circuit currents of different characteristics, a translatingdevice, and a selective disabling device normally opaque to all thecurrents and holding the translating device out of operative connectionwith the circuit, but adapted to automatically change its conditionunder the influence of changing currents to become transparent thereto,to permit them to pass and actuate the translating device.

32. In a signaling system, a circuit having a signal and ahigh-resistance cohering device included in it, said signal and coheringdevice, a source of current, and means operable through the circuit toreduce the resistance of the cohering device and cause the operation ofthe signal by the source of current.

v 33. An electric system comprising a circuit, sources of alternatingand of direct currents adapted to be connected thereto, a selectivedevice in the circuit normally opaque to all currents, but automaticallychanging its condition under the influence of alternating currents tobecome transparent thereto, and a IIO translating device operable byalternating force having suitable characteristics on the currents in thecircuit. circuit to cause the passage of a working cur- 34. In anelectric system, a circuit, a selectrentthrough the selective device andthe cirive device in connection with said circuit, cuit. 5 normallyopaque to the passage of electric In testimony whereof I affix mysignature I5 currents,but adapted to automatically change in presence oftwo witnesses.

its condition and become transparent to elec- EDWARD E. CLEMENT. triccurrents under the influence of some im- Witnesses: pressedelectromotive forces but not of others, I EDWIN S. CLARKSON,

to together With means to impress electromotive l 1). W. EDELIN.

